There is quite a list a devices that won’t get an official update to Marshmallow, like the Galaxy S3, LG G2, HTC One M7, etc. These are basically device a tad older than 2 years now are pretty good hardware-wise.
Which is why users of those Android flagships of past year are looking very, very optimistically towards custom ROM scene, where the like of CM13 and AOSPA can, and are gonna, get them to Marshmallow.
And that’s nothing wrong to hope for.
We’ve got some happy news for you, fellas. It’s been reported that the Marshmallow based AOSPA ROM are already under development.
We can’t really throw a release date at the moment, but it should be before this month’s end that we see a Marshmallow AOSP build appear for one of the Nexus device or OnePlus One.
If you are concerned whether your device will get the Marshmallow based AOSPA or not, then chances are that it will if it had 5.1.1 based AOSPA available.
Otherwise, your device must be locked, or not developer friendly, probably running Exynos processor by Samsung.
Anyway, we hope to share the AOSPA build with you that are based on Android 6.0 Marshmallow. Keep watching this space.